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Abstract:

A method for monitoring a controller for controlling and/or monitoring a
three-phase electric motor, in particular an asynchronous or synchronous
motor, wherein two phase currents are measured and an error signal is
generated if at least one of the two measured phase currents is
essentially zero. An error signal is also generated if none of the two
measured phase currents is essentially zero, but a sum formed of the two
measured phase currents is essentially zero.

Claims:

1-10. (canceled)

11. A method for monitoring a controller for controlling a three-phase
electric motor and/or for monitoring the three-phase electric motor, said
method comprising the steps of: measuring two out of three phase
currents; checking whether one of the two measured phase currents is
essentially zero; generating an error signal when at least one of the two
measured phase currents is essentially zero; checking whether both of the
two measured phase currents are essentially not equal to zero; forming a
sum of the two measured phase currents; and generating an error signal
when the formed sum of the two measured phase currents is essentially
zero.

12. The method of claim 11, wherein the three-phase electric motor is an
asynchronous motor or a synchronous motor.

13. The method of claim 11, further comprising the step of incrementing a
first counter when an error signal occurs.

14. The method of claim 13, further comprising the step of incrementing a
second counter when the first counter repeatedly exceeds a first
threshold within a defined period.

15. The method of claim 14, further comprising the step of detecting a
loss of at least one phase current of the three phase currents when the
second counter exceeds a second threshold.

16. The method of claim 13, further comprising the step of incrementing
the second counter and starting a timer when the first counter exceeds a
first threshold within a defined period.

17. The method of claim 13, wherein the first counter is reset when
exceeding the first threshold.

18. The method of claim 14, wherein the second counter continues to be
incremented as long as the first counter exceeds the first threshold
within the defined period.

19. The method of claim 16, wherein the defined period of time is a
specifiable timer time of the timer.

20. The method of claim 11, wherein the electric motor is used to operate
a household appliance.

21. The method of claim 11, wherein the electric motor is used to operate
a dishwasher or a washing machine.

22. A household appliance, comprising a facility for carrying out the
method of claim 11.

23. The household appliance of claim 22, constructed in the form of a
dishwasher or a washing machine.

24. A household appliance, comprising: an electric motor having three
phase windings connected in a star configuration for operating a
component of the household appliance; a current measuring device
configured to measure a phase current of at least two of the three phase
windings; a detector circuit which checks whether the measured phase
currents have non-zero values and generates an error signal if: one of
the at least two measured phase currents is essentially equal to zero; or
if none of the at least two measured phase currents is essentially equal
to zero, but if a sum formed of two measured phase currents is
essentially zero.

25. The household appliance of claim 24, further comprising a
field-oriented vector controller for controlling operation of the
electric motor.

Description:

[0001] The invention relates to a method for monitoring a controller for
controlling a three-phase electric motor and/or for monitoring the
electric motor, especially an asynchronous or synchronous motor.

[0002] The use of single-phase split-pole motors in dishwasher drain pumps
is known. These motors are designed for a discrete operating point and
are directly connected to an electrical mains voltage. The loss of the
single phase leads to the motor stopping and can be immediately
recognized from the absence of the phase current.

[0003] The underlying object of the invention is to specify a method to
enable the functions of a controller for controlling an electric motor
and/or the functions of the electric motor, especially of a household
appliance, to be checked. In particular an electric motor is to be used
which possesses more versatile characteristics by comparison with the
split-pole motor mentioned above.

[0004] This object is inventively achieved by the method for monitoring a
controller for controlling a three-phase electric motor and/or for
checking the electric motor, especially an asynchronous or synchronous
motor, comprising at least the following steps: Measuring 2 phase
currents (ia, ib)

[0009] Generating an error signal if the sum formed of the 2 measured
phase currents (ia, ib) is essentially zero.

[0010] In the system described here the measured currents are investigated
in respect of a possible error combination in respect of whether one of
the measured currents is zero and the other is not and/or the sum of the
measured currents is essentially zero. If at least one of the conditions
is fulfilled an error signal is output that indicates that the controller
and/or the electric motor is or are not operating correctly.

[0011] In this context it should be noted that if a phase is missing, the
phase current in the missing phase is zero and in the two other phases is
an opposed current of equal size (phase opposition). Since the two phase
currents are sine-wave currents, which each have a value of zero every
180° and since the three-phase currents also each have the value
zero every 180°, account must be taken in the inventive method
that the condition "is zero" is permitted for a certain period of time
and does not provide any information as to functional capabilities. The
current measurement of the phase currents mentioned is also subject to a
tolerance so that preferably limits (of a tolerance band) will be defined
within which a phase current can be assumed to be zero. Likewise limits
(second tolerance band) are specified within which the difference between
two phase currents must lie in order to identify the two phase currents
as opposing each other, It is always sufficient in the inventive method
to only measure two of the three-phase currents, since the three phases
of the synchronous motor are connected in a star configuration. Since the
sum current of the node point of the star circuit is zero the entire
three-phase system can be detected from the two measured phase currents,
thus the absent phase winding current or phase current can be determined.
If the phase is missing a distinction must be made as to whether one of
two current measurement facilities which carry out the current
measurements is positioned in the associated phase winding, or whether
this phase winding is the one to which no current measurement facility is
assigned.

[0012] Preferably a second counter is incremented if, within a defined
period of time, the first counter exceeds a first prespecifiable
threshold value a number of times.

[0013] Preferably the loss of at least one phase current, i.e. the failure
of at least one phase of the asynchronous or synchronous motor, is
detected if the second counter exceeds a second, especially
prespecifiable threshold value. This method provides high reliability in
the detection of the loss of at least one phase of the synchronous motor.

[0014] In particular the second counter can be incremented and a timer
started if the first counter exceeds the first threshold value. The first
counter is preferably reset if it exceeds the first threshold value. The
second counter is especially further incremented if, within the defined
period of time, the first counter exceeds the first threshold value least
one further time. Depending on the reliability of the information, there
can be provision for the first counter to have to exceed the threshold
value not just one further time but more than twice. The said defined
period of time especially involves a prespecifiable time period of the
said timer.

[0015] The invention further relates to a facility for functional
monitoring of an electric motor of a household appliance, especially for
carrying out the method mentioned above, whereby the electric motor is
embodied as a three-winding, three-phase, permanently-excited synchronous
motor connected in a star configuration and is provided with a field
oriented vector regulation, and two phase currents are measured by means
of a measuring device and the measuring results are analyzed by means of
the detector circuit for monitoring the speed of the synchronous motor
and/or for monitoring a presence of all phase currents in the phase
windings of the synchronous motor.

[0016] The invention further relates to a household appliance, especially
a dishwasher or a washing machine, whereby the household appliance is
provided with a facility of the said type.

[0017] The drawings illustrate the invention and the figures are as
follows:

[0018]FIG. 1 shows a structure diagram which allows the functions of
asynchronous motor to be monitored and

[0019]FIG. 2 shows a regulator set circuit diagram of a vector regulation
for a three-phase, permanently-excited synchronous motor.

[0020] The invention is based on a three-winding, three-phase,
permanently-excited synchronous motor of a household appliance,
especially of a dishwasher or washing machine, with the synchronous motor
for example driving a pump of the household appliance which serves as a
drain pump and/or as a recirculation pump.

[0021]FIG. 1 depicts three phase windings 100, 101 and 102 of a
three-winding, three-phase, permanently-excited synchronous motor 108,
with the three-phase windings 100 to 102 being connected together in a
star configuration 103. Each of the phase windings 100 and 101 is
assigned a current measuring facility 104, 105 which measures the
associated phase currents ia and ib. The phase currents ia and ib are
converted by means of a device 106 into component currents iα,
iβ, especially transformed. The two phase currents ia, ib and/or the
two component currents iα, iβ are supplied to a detector
circuit 107 which undertakes monitoring of the speed n of the synchronous
motor 108 and/or monitoring for the presence of all three phase currents
in the three-phase windings 100, 101, 102 of the synchronous motor 108.
Since the sum current in the star point 103 is zero it is sufficient only
to measure the phase currents ia and ib in the two phase windings 100 and
101. The phase current in phase winding 102 can then be calculated. To
clarify terminology it should also be pointed out that "phase windings"
are referred to if the physical operative system is involved and "phases"
if the process involves generating a voltage system.

[0022] The synchronous motor 108 is controlled with a so-called
field-oriented vector regulation. The two phase currents ia and ib are
used for this purpose, in order, taking into account a motor model of the
synchronous motor 108, to be able to control said motor with a
three-phase pulse width modulated voltage system. The frequency, the
phase position and the amplitude of this voltage system can be adjusted.
Power is consequently fed to the synchronous motor 108 with a so-called
modulator.

[0023] The phase winding currents ia, ib, which can also be referred to as
phase currents, are--as mentioned--measured with the aid of the two
current measurement facilities 104 and 105. The two current measurement
facilities 104 and 105 each have a shunt resistor, with the voltage drop
occurring at the respective shunt resistor being directly proportional to
the associated phase current ia or ib respectively.

[0024]FIG. 2 illustrates the regulation circuit for field-oriented vector
regulation with the aid of a regulator set circuit diagram. The two phase
winding currents ia, ib are measured from the three-phase current system,
having currents offset by 120°. This is done with the current
measurement facility 104, 105 in accordance with FIG. 1. With the aid of
a Clark transformation labeled 1 (device 106 in FIG. 1) the two real
phase currents ia, ib offset by 120° are converted into a complex,
stator-oriented orthogonal coordinate system, meaning that a two-phase
90° system is now present comprising the component currents
iα and iβ. These two component currents iα and iβ
are inverted with the aid of a Park transformation labeled 2 via the
rotor angle φ into the rotor coordinate system. This results in the
rotated current components id and iq, with id corresponding to the
magnetization current and iq to the torque-generating current of the
synchronous motor. These current components id and iq are regulated in
the downstream regulator stages 3 and 4 to different setpoint values id
setp and iq setp. Subsequently an inverse transformation is undertaken
which is identified by the reference character 5 and which, as well as
the component voltages uα and uβ for a motor model 6, also
delivers amplitudes for a modulator 7. The modulator 7 involves an
element which is able to generate a three-phase pulse width modulated
voltage system of which the frequency, phase position and amplitude are
adjustable. Such a modulator 7 is also referred to as a converter. For
providing the amplitudes of the component voltages uα and uβ
an absolute value generator 8 is provided on the input side of the
modulator 7. The already mentioned rotor angle φ (rotor displacement
angle) is not measured directly at the synchronous motor 108 but computed
with the aid of the motor model 6 from the component currents iα
and iβ and the component voltages uα and uβ. The motor
model 6 emulates the synchronous motor 108. From the temporal
differentiation of the rotor angle the speed n is computed. This is
indicated by the reference character 9. From the speed n, with the
knowledge of discrete modulation step times, a current angle step for the
modulator 7 is computed. Since at the start point of the synchronous
motor 108 no current and speed information is available, the synchronous
motor 108 will be started up in a controlled manner. For this purpose a
ramp model labeled 10 is provided, which generates a current target speed
and a current angle step in accordance with a start ramp incline. The
setpoint values for the two current components id and iq are specified as
fixed values. FIG. 2 contains three switches 11, 12 and 13, which each
assume a position necessary for starting up the synchronous motor 108.
Once the synchronous motor 108 has started up, it is switched over.
During start-up the modulator 7 runs through a sine wave table for
generating an output voltage pattern with the angle increment of the ramp
of the ramp model 10 and the amplitude from the current regulator
circuits of the setpoint start-up values. If a defined speed n is reached
at which the winding current values ia, ib can be safely measured and the
motor model 6 safely calculated, a switchover is made from controlled
into regulated operation, meaning that the switches 11 to 13 are switched
over and a synchronization point is produced. A speed regulator 15, which
is embodied as a PI regulator, now computes in accordance with an
existing speed variation a setpoint value iq setp for the current
component iq generating the torque. The magnetizing current component id
is regulated to zero.

[0025] In respect of the measurement of the phase currents iα and
iβ it should be pointed out that these are measured with the aid of
the two shunt resistors of the current measurement facilities 104, 105 in
the foot points of the motor windings of the synchronous motor 108. A
half bridge circuit is especially provided in the modulator 7. The
voltage drops and the two shunt resistors are rapidly adapted with the
aid of two fast amplifier circuits to a voltage measurement range of a
microcontroller from 0 V to 5 V. The amplifier circuits are identically
constructed and are dimensioned so that a voltage measurement within the
framework of a pulse width modulation without distortion is possible.
Since in the two foot points positive and negative currents of the same
amplitude have to be measured, the amplifier circuits each possess an
offset voltage which is to be found in the middle of the possible control
range. The respective offset voltage is constantly measured when the
motor is stopped and is checked for plausibility. To minimize the
influence of faults, the offset voltages are filtered by SW lowpasses. In
the event of an implausible offset voltage, converter software assumes an
error state in which control of the pump is not possible.

[0026] The phase currents ia and ib are sampled under interrupt control
carried out with pulse-width-modulation frequency of a pulse width
modulator of the converter. The sampling time lies in the middle of the
control of three low-side power semiconductors of the converter. At this
point in time the three motor windings of the synchronous motor 108 are
short-circuited via the power semiconductors and a freewheeling current
of the motor windings can be measured. Since the triggering of the
sampling lies precisely in the middle of the impulse, the influence of
faults as a result of pulse width modulation switching flanks is
minimized. During a pulse width modulation cycle only one current is ever
sampled. The two currents are measured offset in time by the pulse width
modulation cycle time before the calculation of the motor model. It is a
requirement in this case that the current in the phases of the
synchronous motor is constant during a pulse width modulation cycle time.
The pulse width modulation frequency is selected so that this condition
is fulfilled. The currents are detected with an analog-digital converter
resolution of 10 bits. With this resolution the peak-to-peak value of the
phase currents is mapped.

[0027] A modulation of output voltages of the converter is implemented in
accordance with a look up table (LUT) method. The current angle of the
output voltage is stored in a phase accumulator (16-bit) and corrected
cyclically every 600 ps by a regulation algorithm. Between the
corrections a modulation angle is continued with a constant angular
speed. The LUT has a resolution of 16 bits and is stored with 256
checkpoints in a flash memory of a controller. The pulse width modulation
values are updated in each second pulse width modulation cycle. The
output voltages are corrected with the aid of an intermediate circuit
voltage of the converter during each modulation value computation. This
enables an influence of a voltage ripple in the intermediate circuit of
the converter to be largely compensated for.

[0028] As explained above, a transformation step is undertaken in the said
field-oriented vector regulation in order to convert the phase winding
currents ia and ib into the component currents iα and iβ. This
transformation step is purely algebraic and does not contain any models.
As mentioned, the component currents iα and iβ describe the
three-phase current system in an orthogonal presentation. An angle with
stator reference is computed from the two component currents iα and
iβ. The measurement is repeated at defined time intervals. The
spacings are preferably selected such that they satisfy the requirements
of error detection. From the ongoing measurements, by differentiation of
the angle in accordance with the time an angular speed is computed and as
a consequence thereof a speed n of the synchronous motor 108. Preferably
the angle difference of adjacent angles and the time difference of
adjacent times are formed and the angle difference is divided by the time
difference for the differentiation.

[0029] Since current samples can be discarded, which means that the time
association of two current samples for ia and ib can change and the
measurement is more imprecise in the lower speed range, the speed can
preferably be filtered. As an alternative to filtering it is advantageous
to apply a selection criterion. Provided y-values of x-values correspond
to a default, it is assumed that the result is correct.

[0030] As already mentioned, the three phase windings 100 to 102 of the
synchronous motor 108 are connected in a star configurations. Since the
sum current of a node point is zero, it is thus sufficient to measure two
of the three phase windings. This has already been explained with
reference to FIG. 1. If a phase is missing, i.e. if a phase current of a
phase fails, a distinction must be made as to whether one of the two
current measurements is positioned in this phase or whether this involves
the non-measured phase. A check should thus be made whether one of the
two current measurement facilities 104, 105 lies in this phase or not.

[0031] If a phase is missing, the current in the missing phase, i.e. in
the phase winding concerned, is zero and in the other two phases/phase
windings is opposed and equal in size. So-called phase opposition is thus
present. Since the two phase currents ia, ib are each zero every
180° (sine-wave currents) and also the three-phase currents are
each zero every 180°, account must be taken during measurement for
zero current of the fact that this state is allowed for a certain period
of time. The current measurements by means of the current measurement
devices 104 and 105 are each subject to a tolerance, so that certain
limits must be defined within which a current is assumed to be zero.
Likewise limits are needed within which the difference between two
currents can lie in order to identify the two currents as opposing one
another. In the first case a first tolerance band is defined as limits
and in the second case a second tolerance band. To monitor the
completeness of the phase windings of the synchronous motor 108, i.e.
whether at least one phase of the synchronous motor 108 has failed, the
two measured currents ia and ib are investigated in respect of the
following possible error combinations: a) if one of the two measured
phase winding currents ia, ib lies within the first tolerance range, this
phase-winding current is assumed to be zero, b) if the difference between
the two measured phase winding currents ia, ib lies within the second
tolerance range, the two measured phase winding currents are assumed to
be opposing one another in phase opposition.

[0032] In step a) an investigation is undertaken as to whether one of the
two currents ia, ib lies below the zero-current limit defined by the
first tolerance band. In step b) an investigation is undertaken as to
whether the difference between the measured currents ia, ib lies below
the phase opposition limit defined by the second tolerance band.

[0033] Basically it should be pointed out that in principle it is simpler
to detect a zero current than a phase opposition. If one of the two said
events occurs, a first counter is incremented, especially increased
weighted in accordance with the type of event. If a measurement fulfils
neither the one nor the other criterion, the first counter is reset.

[0034] If this first counter exceeds a first threshold, a second counter
is incremented and the first counter is reset and also a timer is
started. If within a defined period of time, especially the specified
timer time, the first threshold value of the first counter is exceeded a
second time or at least a second time, the second counter is incremented
again. If this situation does not occur, the second counter is reset. If
the second counter exceeds a second threshold value, loss of a phase,
i.e. the absence of a phase-winding current in a phase winding 100, 101,
102, is detected.

[0035] To summarize, it can be stated for the method for speed detection
that the component currents iα and iβ of a transformation step
of the field-oriented vector regulation are used without any model
creation. Stator-oriented angles are always computed at at least two
defined points in time, with the time difference only having to satisfy
the accuracy requirements for detecting the stationary state (taking
account of the subsequent filter/the subsequent analysis). This is
followed by the computation of the speed (approximated speed) from the
temporal differentiation of the angle. In addition a weighting of the
speed information (especially y of x speed values within a tolerance) is
undertaken.

[0036] The check for completeness of the phase windings measures two phase
winding currents of the star-connected synchronous motor. A weighted
increase of a first counter is undertaken if either a current lies below
a zero current threshold or the difference between two currents lies
within a phase opposition threshold. A second counter is increased if the
first counter exceeds a (first) threshold of the first, weighted counter
within a defined period of time. The loss of a phase is detected if the
second counter exceeds a (second) threshold assigned to it.